The present invention relates to a process for producing an iodinated aromatic compound at a low cost and a high purity.
Iodinated aromatic compounds are used as an important intermediate in the production of organic photoreceptors to be used for electrophotography, organic electroluminescent device or the like, dyestuffs, agricultural chemicals, pharmaceuticals and the like.
Iodinated aromatic compounds can generally be synthesized by the Sandmeyer reaction of corresponding aromatic amino compounds (Bull. Soc. Chem., 7, 634(1940)) or by directly iodinating aromatic compounds.
The process using the Sandmeyer reaction is not industrially preferred, because aromatic amino compounds employed for the reaction tend to have strong toxicity and moreover, post-treatment after reaction is complicated and a production yield is low.
In the latter process for directly iodinating an aromatic compound, on the other hand, an oxidizing agent and if necessary, a reaction solvent and an acid catalyst are used upon reacting the aromatic compound with an iodine compound. Concerning the use of an oxidizing agent, conventionally known are a process using peracetic acid (J. Am. Chem. Soc., 90, 6187(1968), J. Chem. Soc. Perkin I, 180(1972)), a process using iodic acid (Ann., 634, 84(1960)), a process using periodic acid (Journal of the Chemical Society of Japan, 92(11), 1021(1971)), and a process using a silver salt such as silver nitrate or silver sulfate, or silver trifluoroacetate (J. Am. Chem. Soc., 73, 1362(1951), Tetrahedron Lett., 30 (29), 3769(1989), Synth. Commun., 20(6), 877(1990)). The use of such an oxidizing agent increases a cost, because it is expensive and the disposal of its waste liquid is required.
A process using nitrogen dioxide (U.S. Pat. No. 4,567,280) and a process using nitric acid (J. Org. Chem., 42(25), 4049(1977)) as an oxidizing agent are also known. These processes are however accompanied with the problems in that an aromatic nitro compound is byproduced when such an oxidizing agent is used, which makes the purification difficult, and an oxidized nitrogen gas is generated from the reaction system or some aromatic nitro compounds byproduced have strong toxicity, leading to difficulty in taking countermeasures against environmental pollution.
Further, a process (JP-A-63-91336) using hydrogen peroxide and a process (JP-A-49-14527) using a persulfate are known. These oxidizing agents however need care upon handling and do not bring about a high yield.
When a large excess of an aromatic compound is used relative to an iodine compound as in mono-iodination (U.S. Pat. No. 5,856,596), the aromatic compound which has remained after reaction must be separated by post-treatment. When the aromatic compound has a high boiling point, separating operation such as solid distillation using special equipment becomes a cause for a high cost.
An object of the present invention is to provide a process for producing a high-purity iodinated aromatic compound at a low cost, while neither using a highly toxic raw material nor substantially forming a byproduct.
In the present invention, there is thus provided the below-described process for producing an iodinated aromatic compound and the object of the present invention is attained by the process.
That is, the present invention provides a process for producing an iodinated aromatic compound, which comprises reacting an aromatic compound with an iodine compound in the presence of a chlorate as an oxidizing agent.